linux-kernel - Re: [PATCH -tip 2/2] [BUGFIX] kprobes/x86: Fix removed int3 checking order

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Date:	Wed, 28 Apr 2010 08:30:04 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Dave Anderson <anderson@...hat.com>
Subject: Re: [PATCH -tip 2/2] [BUGFIX] kprobes/x86: Fix removed int3
	checking order

On Tue, Apr 27, 2010 at 06:33:49PM -0400, Masami Hiramatsu wrote:
> Fix kprobe/x86 to check removed int3 when failing to get kprobe
> from hlist. Since we have a time window between checking int3
> exists on probed address and getting kprobe on that address,
> we can have following senario.
> -------
> CPU1                     CPU2
> hit int3
> check int3 exists
>                          remove int3
>                          remove kprobe from hlist
> get kprobe from hlist
> no kprobe->OOPS!
> -------

Do you have a testcase for this issue?

> This patch moves int3 checking if there is no kprobe on that
> address for fixing this problem as follows;
> ------
> CPU1                     CPU2
> hit int3
>                          remove int3
>                          remove kprobe from hlist
> get kprobe from hlist
> no kprobe->check int3 exists
>          ->rollback&retry
> ------

You may also want to fix up the comment on top of kprobe_handler() about
the interrupt gate as its only true for x86_32 and not x86_64, right?

> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Dave Anderson <anderson@...hat.com>
> Cc: Ingo Molnar <mingo@...e.hu>

Acked-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
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